1. Field of the Invention
The invention relates to the field of optical recognition of barcodes. In particular, it relates to a method and to a portable apparatus for the optical detection of a linear barcode pattern and for determining a symbol sequence which is coded by the barcode pattern, according to the preamble of the respective independent patent claims.
2. State of the Art
Methods and apparatus for the optical detection of a linear barcode pattern, in particular those with which the portable apparatus are mobile telephones with cameras, are known. Thereby, as a rule, it is to be assumed that the pictures which are taken by the camera are adequately focussed, for example because the camera has an auto-focussing function. Such methods however fail with cheaper cameras with fix-focus lenses, since the cameras do not provide a focussed picture with an object distance which is necessary for an adequately defined picture of a barcode or line code.
Ideas for processing blurred or indistinct pictures for the recognition of barcodes exist. These are known for example from the following publications:    J. Kim and H. Lee, “Joint nonuniform illumination estimation and deblurring for bar code signals”, Opt. Express 15, 14817-14837 (2007)    Ta-Hsin, Ke-Shin Lii, “Deblurring Two-Tone Images by A Joint Estimation Approach Using Higher-Order Statistics”, Proceedings of the 1997 IEEE Signal Processing Workshop on Higher-Order Statistics (SPW-HOS '97), page: 108, year of publication: 1997, ISBN: 0-8186-8005-9    S. Esedoglu, “Blind deconvolution of bar code signals” Inverse Probl. 20, 121-135 (2004).
The described methods however are very computation-intensive, so that for example minutes are required for the analysis of a picture. Moreover, the recognition with regard to pictures of a quality, as is provided by a defocused mobile telephone camera, is not reliable or not at all possible.